Common-batteby automatic telephone system



T. G. MARTIN.

common BATTERY Auommc TELEPHONE SYSTEM.

APPLICATION FILED IAN. 4,1906- RENEWED .IULY 2,19I9.

` Patented Mar. 2, 1920.

5 SHEETS-SHEET I.

IIITIIII "T. G. MARTIN. COMMON BATTERY AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED IAN. 4,1906- RENEWED .IULY 2| T919- 1,332,226. Patented Mm. 2, 1920.

5 SHEETS-SHEET 2.

T. G. MARTIN. COMMON BATTERY AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED JAN.4|190. RENEWED JULY 2,11919.

Patented Mar. 2, 1920.

5 SHEETS-SHEET 3.

409X 406xi l 4219: i 45p /4/ I s/ l i T. e. MARTIN. l COMMON BATTERY AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED JAN. 4,1906. RENEWED JULY 2| I9I9.

1 ,332,226. PatentedMar. 2, 1920.

5 SHEETS-SHEET 4.

T. GQMARTIN.

COMMON BATTERY AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED TAN. 4.1906. RENEWED JULY 2.1919.

UNITED STATES PATENT OFFICE..

TALBOT G. MARTIN, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, T0 AUTOMATIC ELECTRIC COMPANY, A CORPORATION OF ILLINOIS.

COMMON-BATTERY AUTOMATIC TELEPHONE SYSTEM.

Application led January 4, 1906, Serial No. 29.4;,663

T0 @ZZ @07mm t may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Common-Battery Automatic Telephone Systems, of which the following is a specilication.

My invention relates to telephone systems in general, but more particularly to automatic or semi-automatic telephone systems, and especially to telephone systems of that particular character in which the subscribers of one common battery exchange may call up and obtain connection with the subscribers of another common battery exchange, and wherein the expedient for electrically calling the number of the called subscriber consists in the transmission of electrical im pulses from the calling subscribers station to the exchange or central station where the automatic. trunk-selecting and line-connectingl machinery is located and arranged under the direct control of the different subscribers.

Generally stated, the object of my invention is the provision of an improved and highly etlicient telephone system of the foregoing general character.

Special objects of my invention are the provision of an improved common battery apparatus for automatic or semi-automatic telephone systems; the provision of an im proved repeater for use in making a trunkline connection between two common battery automatic telephone exchanges; the provision of an improved connector or line-connecting machine for use in a common battery automatic telephone exchange, and adapted more particularly for use iu connecting up the subscribers of one exchange withl those of another exchange; the provision oi various improved line and auxiliary circuits for use in connecting one subscriber with another-preferably subscribers of common battery automatic telephone exchanges-as will hereinafter more fully appear: and the provision of certain details and features of improvement tendiurr to increase the general eiiiciency and serviceability of a telephone system of this particular character.

To the foregoing and other useful ends, mv invention consists in matters hereinafter fullv described and claimed.

In Figure l a substation #7000 is repre.-

Speccation of Letters Patent.

Patented Mar. 2, 1920.

Renewed July 2, 1919. Serial No. 308,271.

sented connected with a first-selector F1 and with a repeater R, which two instruments, it will be understood, are part of the apparatus of a central station designated as central station #1.

Fig. 2 shows a second-selector S connected with a connector C of my improved design, and the connector connected in turn with the substation #2420, which latter is designed to represent the called sub-station, and which is directly connected with the first-selector F2, said sub-station #2%20, it will be seen, being a member of the exchange system that comprises the central station apparatus shown in Fig. 2, and which will be known as central station #2.

Figs. l and 2 taken together represent the sub-station #7000 connected with the substation #2420 of the distant exchange, and which former, in the establishment and maintenance of the connection, employs the first-selector Fi and the repeater R at its own central station #1, and the sec0nd-se lector S, a connector C and the called firstselector F2 at the central station #2.

Fig. 3 is a diagrammatic perspective view of the first-selector F1.

Fig. 4l likewise represents the connector C.

Fig. 5 is a simplified diagram showing the distribution or supply of talking current to the subscribers lines.

Each central has a battery of its own for the operation of its apparatus. Central station #l has a battery B1 and central station #2 has a battery B2. The sub-stations employed in connection with common battery systems of the nature in question are all of a well-known and suitable type. Sub-station #7000, tor instance, is at once recognized by the peculiar switch-hook 2 which is with a number of cam-like arms 3, el, and 6. The primary circuit at said station, when in use. is bridged across the main line. and comprises in series the primary winding 7 of the induction-coil 8, a transmitter 9. a couple of springs 10 and 11 identiiied with the signaling button l2, and two springs 13 and lllby means of which the said circuit is maintained closed or opened, dependingupon whether the hook is up or down. Said hook is Divoted at one end by the screw 15, andis forced to rise. whenever the weight of the receiver 16 is removed from it. by a suitable switch-liool -sprin not shown, The secondary circuit, auxiliary to the primary, comprises the said receiver in series With the secondary winding 17 of the induction-coil 8, in a permanently closed inductive local circuit. The ringercircuit at said sub-station includes the ringer 18, the ringer-circuit-springs 19 and 20 and the condenser 21. The circuit, while the switch-hook is down, is closed by the camarm 4 that presses the said ringlng-circuitsprings into contact, and is normally bridged across the main line. While the hook is up, however, the said bridge is open because the said springs 19 and 20 spring apart after the cam-arm 4 is removed from the spring 19. The cam-arm 5 controls the continuity of a ground-circuit between the so-called groundpost 22 and ground-terminal G3, b means of two springs 23 and 24 that are included in said circuit. The sub-station has three other springs 25, 26 and 27 which are known as the release-springs and by means of which the main line-conductors may be grounded simultaneously for the purpose of restoring the exchange apparatus in a manner that will be explained. When the hook is depressed, and as it descends, the said releasesprings are forced together by the cam-arm 3, which latter then engages the laterallyrojecting extremity 28 of the spring he engaging portions of the cam 3 and spring 25 are constructed with their surfaces at an angle with each other, so that as the hook goes down one surface of the projection 28 is engaged by the cam-arm, and when it rises the opposite surface is met. In this way, when the hook goes down, the spring 25 is forced into electric connection with the springs 26 and 27, and when the hook ,rises it is shoved in the opposite direction.

It should be clear that at the limit of each stroke of the hook the cam-arm 3 clears the s ring 25. The calling device employed by t e subscriber may be of any suitable or desired character. The type illustrated, however, comprises two push-buttons 29 and 30, two contact-points 31 and 32, two springs 33 and 34 and the ground-post 22. The spring 33 and contact 31 are normally in contact, as well as the spring 34 and contact 32. But when the button 29 is pressed, the spring 33 is separated from the contact-point 31 and connected with the ground-post 22, and When the button 30 is pressed the second spring 34 is pressed onto the same groundpost, after said spring leaves the contactpoint 32. The signaling button 12 has a grounded contact-point 35 associated with it onto which the spring 11 is forced whenover the said button is pressed.

In Fig. 3 the first-selector I"1 is shown with the bank 50 of trunk-line-terminals beneath it, while the private-bank 51 is located just above the trunk-line-bank. The switch-shaft 52 is vertically disposed on the front of the switch-frame and` retained con-1 nected therewith by bearings which are not shown. The shaft may be moved endwise in said bearings and then rotated by ratchet and pawl electro-magnetically-operated mechanism, the endwise step-by-step movements occuring first. Among the functions of the shaft, an important one is the holding of the line-wipers 53 and 54, and of the private-wiper 55. The former two comprise a set distinct from the latter, but both sets are located within range of the contacts of their respective banks 50 and 51. Said wipers are not only insulated from the sha t, but from each other as well. Among the details that are associated with the shaft is a cam-piece 56 which is of a split sleeve design and secured to the shaft by a screw 57. The general shape of said cam, in section at right angles to the shaft, is that of an oval with the sharper apex on the side farthest away from the said screw. Said cam abuts on a hub 58 that is shrunk to the shaft near the middle of the latter. This hub carries a set of longitudinal teeth 59 that serve, as will be disclosed, to enable the forward rotation of the Shaft, and as a locking means against backward rotation of same. On the neck portion of said hub there is found a set of circular teeth 60 that serve in turn as a means by which the raising of the shaft is accomplished, and for locking it when raised. rlfhese circular teeth are traversed by a groove 61 into which the end of a socalled shaft-rest 62 normally projects; but when the shaft is rotated any one of the said circular teeth which may be at the proper height slides onto the end of the rest. The end of said rest, of course, is adapted to fit the circular grooves between said circular teeth. The upper surface of the engaginv end is level, but the under side is chamfered to form a wedge that corresponds to the upper slope of the circular teeth. Above the hub 58 the shaft carries an arm 63, known as the normal-post-arm, which, while the switch-shaft is at rest, and While the shaft-rest occupies the slot 61, is retained against thenormal-post 64 by the coiled spring 65. The said normal-post-arm normally retains an of-normal-spring` 66 in contact with a contact-point 67, located beneath it, but when the shaft is raised said spring iexes into contact with a grounded contact-point 68 instead. Among the magnets allotted to the first-selector some are used as relays and others as operating magnets. The magnets 69 and 70 are among the former kind and are known as the vertical and rotary line-relays. By means of their respective armatures 71 and 72 the springs 73 and 74 are controlled with respect to the ,around-spring 75. Said springs are comprised in energizing circuits of operating magnets that raise and rotate the shaft. The magnet 76, armature 77, and springs 78, 79

and 80 constitute the bridge-opening-relay, or bridge-cut-ofbrelay as it is called, and the macnet S1 with its armature 82 and springs 83 and constitutes the back-release-relay, which ifi used for restoring the switch after it has soir/.ed a trunleline. Oi the operating magnets the magnet S5 is known as the vertical-magnet and has allotted to it a socalled rcrtictil-armature 86 that is supper4 nl by pito 87. lWhenever the coils 8S and 89 of said vertical-magnet become energized the :n 'matui'r 90 is attracted, and when the magnetization ceases the retracting spring,l 90 restores said armature to its normal position. The upward movement of the armature is limited by the polenpieces of the magnetcoils Sti and 89, and the lower limit is marked ay a section of the switch-frame that passes under the arm 91. Said arm is known as the vertical-arm and extends forwardly from the vertical-armature S6, of which latter it a part. The vertical-arm carries on its endaso-called vertical-pawl 92 which, when the vertical-armature is attracted, engages with some one of the circular teeth 60 to raise the shaft. Normally, the under surface of the upper section of said pawl rests agr-einst a piece that is secured to the switch-A fame, and that retains the pawl away from the circular teeth. When the verticalarmature is attracted, the said pawl rises, a retractingspring 93 thrusts the upward side of the pawl toward the circular teeth 60. 11s soon as said pawl clears its normal-rest, and by the time that the vcrtical-armature strikes the pole-pieces, the vertical-pawl strikes, with the rear surface of its upper section, a bumper piece, which latter constitutes a part of the switch-frame. Thercfmfe, the shaft is thus prevented from being` thrown up more than one notch at a time, by its own momentum. lt is clear, then, tha t the pawl 92 not only raises the shaft, but it also acts as a lock at the end of each stroke. The vertical-arm has also an L-shaped piece 94 on its under edge, that projects under a so-called release-link 95 of `flexible spring material. Said link has an aperture 96 on its front end, and is secured to the armature 97 of one of the operating,` magnets 98 known as the release-magnet. Said armature is suspended from the frame by the supports 99, and is normally retained by the spring 100 away from the poleepiece of the release-magnet. A stop is suitably provided behind said armature to limit its movement when retracted. rllhe iirst-selecvtor is provided with a peculiarly shaped switch-shaft is raised and in normal rotary position, and so that the latter dog 104: may engage with the longitudinal teeth 59 when the shaft is rotated. To the right of the pivots 102 the body of the double-dog eX- tends rearwardly, and projecting down therefrom is an arm 105 that comes into play very prominently during the releasing of the switch. Near its extremity, and on the upper side of said body, a pin or lug 106 projects up. Said lug is normally caught in the aperture 96 of the releaselink 95, and because of the action of the spring 100 through said link the dogs 103 and 101 are retained away from the shaft. Always, at the first stroke of the vertical-armature, the link95 is drawn away from the lug 106 by the piece 94, and then the double-dog is so rotated by the retracting-spring 107 that the dog; 103 falls under the irst circular tooth, in order that when the verticalearmature returns to its normal position the said shaft will be retained by said dog in its new position. The *release-link 95, while the, double-dog is free, rests with its very end upon the luo 106, out of locking engagement with it. lVhe-n the vertical-magnet is energized a second time the shaft is raised a second step and the dog 103 at the second stro te passes from under the nrst tooth t0 below the second tooth, holding the shaft again above. rlhe release-magnet 98 is composed of two coils like the vertical-magnet S5, but for simplicity only one coil is shown. 1f, while the sha-ft is raised, the said releaseanagnet should be energized, the releasearmature 97, of course, is attracted and the release-link 95 thrust forward to catch the lug 106 in the aperture 96. Upon the denergization of the release-magnet the retracting-spring 100 then withdraws the dogs 103 and 10a from the shaft, which latter, beingn deprived of its only support, then falls to normal position by its own weight. After the shaft is once raised it may be rota-ted by a second operating magnet 108 known as the rotary-magnet. Said magnet has two coils 109 and 110 and, unlike the vertical-magnet, has its armature 111 pivoted in a vertical plane. Said armature may be moved` about a vertical axis that passes through the pivots 112. rlhc limit of the movement of said armature toward the rotary-magnet is determined by the pole-pieces of said magnet, which movement is produced by the rotary-magnet itself. The motion of the armature in the opposite direction is produced by the retracting-sprinp; 113 and limited by a switchstop behind the so-called rotary-arm 114. 'lfhis arm, like the vertical-arm, carries a so-called rotary-pawl 115. Similarly to the vertical-pawl, said rotary-pawl normally rests against a stop that retains it away from the longitudinal teeth, and when the rotary-armature is attracted it is drawn into engagement with the longitudinal teeth by a spring 116 that is attached between the rotary-arm and the rear of said pawl. By the time that the rotary-armature strikes the pole-pieces of the rotary-magnet, the rotarvpawl also strikes a bumping post, as does the vertical pawl, and locks the shaft against any further advance by the force of its own momentum. At the end of the first rotary step the dog 104 falls behind the first longitudinal tooth, so that when the rotary-pawl falls back the shaft is retained. It should be evident that, as the shaft is rotated, the vertical-dog 103 is extricated from the groove in which it has been resting, by the passage of the rotary-dog 104 across the longitudinal tooth over which it has to slide at the time. But at the beginning of the rotation, it will be evident that the tooth which has been caught by the vertical-dog slides onto the shaft-rest 62, and in this way the shaft is still held raised after the rotation begins. The rotary-armature is not only provided with a so-called interrupter-finger 117 that separates the interruptor-springs 118 and 119 whenever the rotary-armature is attracted, but also with a rotary-armature-finger 120 that exercises certain controlling influences over the armature 121 of the last one of the operating magnets, namely the private-magnet 122. The said private-armature 121 works in a vibratory manner about a horizontal axis that passes through the supporting-points 123. This armature is formed with a forwardly-projecting arm 124, the latter having two flat surfaces in an approximately horizontal plane. Furthermore, the end of the said arm is bent at right angles downwardly and carries certain mechanical details, namely a lateral arm 125 which is designed to control circuits comprising the private-springs 126, 127 and 128, and a tooth escapement which includes two flexible springs 129 and 130, each of which springs is riveted by one end to the arm 124, one on the upper side and the other on the lower. The upper spring is straight and has formed on its end two tooth projections 131 and 132 which extend down, while the lower one is bent down and at right angles again to the front. This double angle on the lower spring is so designed that the latter may clear the bent portion of the private-arm, against which portion said spring` rests with a degree of tension, and so that there may be space in front of said bent portion to receive two other tooth-shaped upwardly-projecting pieces 133 and 134 that are formed on the forward end of said escapement-spring 130, and which are sustained in juxtaposition to the upper teeth, but slightly to the rear thereof. A retracting-spring 135, suitably located, holds Said amature normally away from the private-magnet pole-piece. Awellknown auxiliary switching mechanism common to such switches is the so-called sideswitch. It is shown 1n connection with the first-selector F1 and comprises an arm 136 which is secured to the switch-frame in such a manner that it may be made to swivel in -a vertical plane about the pivots 137. The right extremity of said arm is drawn out into a finger 138 that works in conjunction with the escapement-teeth previously described. Said teeth, in a manner to be described, convert the outward movement of the side-switch to a step-by-step motion, which movement is produced by a retracting-spring 139. At the base of the finger 138 a lug 140 is bent to the front and adapted to strike the cam 56 at a suitable time. lVhenever the shaft is rotated, however, said cam is carried beyond the. reach of said lugand the finger 138 falls against the tooth 134. Near its left extremity the arm 136 carries a number of wipers 141, 142, 143 and 144, all suitably mounted upon a pin 145 and insulated therefrom and from each other. Said wipers are known as the sideswitch-wipers and are adapted to be operated by the private-magnet and escapement device previously explained. If the private-magnet is energized once the privatearmature is drawn down once and restored to its normal position. The escapement-finger 138 then passes from behind the tooth 133 onto the rear of the tooth 131, at the downward stroke of the private-armature 121, and from behind the latter tooth at the return stroke. As soon as the escapementfinger clears the latter tooth the retractingspring 139 draws the side-switch to the second position where it is stopped by the lug 140 when it strikes the cam 56. Immediately, then, when the rotary-magnet energizes, the shaft is rotated and the cam passes away from the reach of the lug 140; and then the finger 138 of necessity falls against, the tooth 134, because of the tension in the spring 139. The rotation of the shaft results when the rotary-armature 111 is attracted by the rotary-magnet, and at the same time the rotary-armature-finger 120 depresses the private-armature 121 and causes the finger 138 to disengage from the tooth 134, and to advance against the tooth 132. Then, as the rotary-armature returns to normal position, and when the rotarymagnet denergizes, the private-armature, on following the finger 120, permits the escapement-finger 138 to escape from the last tooth 132, thus permitting the side-switch to pass to the third position with the said finger 138 resting against the side-switch-stop 146. In their normal positions the sideswitch-wipers 141, 142, 143 and 144 engage with the contact-points 147. 148, 149 and 150, respectively. This position is known as .the first position of the side-switch, at which time it will be clear the finger 138 is held behind the escapementtooth 133. In the second position, while the said linger is be tween the teeth 133 and 134, the said sideswitclrwipers engage instead with the con tact-points 151, 152, 153 and 154, respectively; and when the said linger138 falls against the stop 146 the wipers change their positions into contact with contact-points 155, 150. 157 and L53, respectively. Between the pivots 137 and the wiper-supporting-pin 1415 a rearwardly-extending arm 159 on the sideswitch-arni 136 pivotally supports on its end one end of a link 160, the other end or' which latter, being biturcated, engages with the lower end ot the double-dog-arm 105 which is constructed somewhat in the shape o'l an inverted T. Should the releasew magnet be energized while the side-switch is in third position, and, of course, while the sha'lt is olii-normal or rotated, the release-link 05, being attached to the releasearmature 97 is thrust forward when the release-armature is attracted, and catches the lug 100 in the aperture 96. Then when said releasearmatnre is restored the spring 100, as before described, withdraws the dog 103 from the circular teeth 60. At the same time the arm 105 drives the link 160 back, which latter then rotates the side-switch-arm 136 about the pivots 137 against the tension of the sidcsswitch retrac'tingspring 139, and thus drives the finger 138 along between the springs 122 and 130 to a position behind the tooth 133, locking the side-switch in the first or normal position. The switch-shaft being unlocked by the removal ot th dog-support 104, and being thus lett free is rotated by the coilesprinp 65 until tl e instant that the end of the shattrest enters the slot 61, at which time the shaiit drops to its normal position. Therefore, after the switch has been operated, the energization and denergization of the release-magnet is sufiicient to restore the switch completely to its normal position. rl`he line and private banks are each provided with ten rows of contact-terininals, cach row consisting of ten sets of contacts. Therefore, the shaft is so constructed that it may be raised to any one of ten levels; at each level it may be rotated ten successive steps in order that the wipers which it carries may be placed in connection with any one of the terminals oi' the ten sets oi contact-terminals in each level. The repeater ll comprises two line-relays 200 and 201 which, through their respective armatures 2022 and 203, operate between them the line-relfry-springs 204., 205 and 206 and the two release-springs 207 and 208. A dirl'erinitial-relay 209 has two windings 210 and 211 one ot which is connected through the vertical-line-relay 200 with the vertical side of the main talking conductors, while the 'other end of said winding 210 is permanently connected with the non-grounded terminal ot battery B. The second winding 211 is connected through the rotary-linere 201 to the rotary side of the main talking conductors, while its other end is connected with a spring 212 ot a so-called polechanging-relay 213. Said spring is normally connected with a second spring 214C that is permanently connected with the nongronnded terminal of battery B; but it may be switched by the armature 215 ot the relay away from said spring 214C and into contact with a third and grounded spring 216. With such construction the differential-coil 210 may be energized only when the vertical side oli the line is grounded, but the other coil 211 may be energized when the rotary side of the line is grounded, or at times when the spring 212 is grounded. In one case the current will flow in one direction, and in the other in the opposite direction, so that the two coils may be energized to neutralize or reinforce each other, depending upon the direction in which the current through the latter coil 211 is made to How. Also, with the arrangement described, the two ends of the coil 211 may be grounded, rendering said coil or winding and the rotary-line-relay 201 short-cirouited through ground for the purposes herein set iforth. Said differential-relay, when ener gized, has the power through its armature 21.7 to separate the springs 218 and 219 and to close the springs 220 and 221. The formounted rigidly with respect to the springs' associated with them, but they may be mounted and arranged on any suitable base and in any suitable manner. A dead-resistance-coil 235 of about 60 ohms is also included in the repeater for purposes hereinat'ter disclosed.

The second-selector S employed with my system is identical with the tiret-selector F1. lflowever, parts like the springs 66, 67 and 03 and the bridge-cut-od-relay 76 are removed altogether. Furthermore, conductors like the ones that terminate in the bridgecnt-oili'elaysprings 78, 79 and 80 are permanently united and the springs discarded.

Fig. l shows the connector C which has many parts and circuits very similar to those of the first-selector. The line and private banks 250 and 251 will be recognized. The switch-shaft 252 is identical with the firstselector-shaft and is, therefore, provided with the line-wipers 253 and 254, the private-wiper255, the cam 256, longitudinal and circular teeth 257 and 258, respectively, the normal-post-arm 259, and the coil-spring 260. The vertical movement of the shaft is, of course, produced by means of the verticalmagnet 261, vertical-arm 262, and verticalpawl 263, the said vertical-arm 262 being supplied with the L-shaped piece 264, as usual. The release-magnet 265, however, has its armature 266 on the right side instead of on the left side, which amature is constructed with an elongated front extremity 267 that reaches as far as the middle section of the body of the double-dog 268. The release-link 269 is under the control of the L-shaped piece 264, and is permanently secured to the switch-frame at the pin 270. The double-dog has the usual vertlcal and rotary locking-dogs 271 and 272, respectively, and the side-switch releasing-arm 273, while on the upper side of the body of the double-dog the lug 274 that is caught by the release-link 269 is in its usual position. When the release-magnet of the connector is energized the release-link 269, instead of being thrust forward to catch the said lug 274, remains where it is and, instead, the double-dog 268 is struck by the armature 266 at a point to the right of the bearings 275 by the end 267, so that the lug 274 is driven under the aperture 276 in which latter it is caught by the release-link 269. The double-dog 268 is thus prevented from returning to its operative position when the release-magnet becomes denergized. The rotary-magnet 277 has a rotary-armature 278 that is quite simple. This latter is provided with only a vertical-arm 279 upon the extremity of which the rotary-pawl 280 is located. The rotation of the shaft is produced in the same mechanical manner described in connection with the first-selector, each time that the rotary-magnet is energized. The private-magnet 281, the privatearmature 282, springs 283 and 284, escapement-teeth 285, 286, 287 and 288 and the arm 289 are identical with the similar parts of the first-selector. The said arm 289, however, controls the private-springs 290, 291, 292 and 293. so that when the private-armature 282 is down the rst two of said springs are separated and the last two brought into contact, and when the said armature is up the reverse takes place-that is, the springs 290 and 291 close and the springs 292 and 293 separate. In the side-switch of the connector the side-switch-arm 294, escapementfinger 295, cam-lug 296, side-switch-stop 297, and retracting-spring 298, on one side of the pivots 299, are similar to like parts of the first-selector side-switch; while the member 300, link 301, side-switch-wipers 302, 303, 304 and 305 together with their corresponding contact-points 306, 307 and 308; 309, 310 and 311; 312, 313 and 314; and 315, 316 and 317 are on the other side of said pivots. Among the relays of the connector the vertical-line-rclay 318, by its armature 319, can Hex the spring 320 against the groundspring 321, and the spring 322 toward the spring 323, when said relay is magnetized. The rotary-line-relay 324, in the same manner, by its armature 325, when the relay is magnetized, forces the spring 326 against the same ground-spring 321, and permits the spring 323 in turn to bend toward the former spring 322. Said two springs 322 and 323 are so adjusted that they come into contact with each other whenever the two armatures 319 and 325 are attracted at the same time. The ringer-relay 199 is a feature common to all connectors of the type under consideration and can, when magnetized, open the connection between the called and the calling line and place across the former the terminals of the ringer-generator J. This operation is accomplished by means of the armature 327 and the ringer-relay-springs 328, 329, 330, 331 and 332. In addition, the connector has two double-wound relays 333 and 334, known as the front and back bridgerelays, the former being differentially wound. Each of these coils comprises two windings 335 and 336, and 337 and 338, respectively. The differential-relay has its windings 335 and 336, respectively, connected with the vertical and rotary linerelays 318 and 324, and through these relays said windings are connected with the main line talking conductors, as will be more clearly pointed out, and said differentialrelay, by its armature 339, and when energized, forces the dierential-relay-spring 340 from the spring 341 against which latter it normally rests and into contact with the third diferential-relay-spring 342. Furthermore, the winding 335 is connected permanently with the vertical line relay 318 between the vertical-line-conductor and the non-grounded terminal of the battery, and is subject to energization only when the vertical-line-conductor is grounded; but the winding 336, while permanently connected with the rotary-line-conductor through the rotary-line-relay 324, by one end, has its other terminal connected with the backbridge-relay-spring 343. This latter spring, when the back-bridge-relay 334 becomes energized, is forced away from its normally engaging spring 344 into engagement with the spring 345, which latter spring is connected to ground each time that the connector side-switch-wiper 303 passes to third position. The spring 344 with which the spring 343 normally engages, it should be noticed,

is permanently connected to the non-ground ed pole of the battery. "With such arrangement, the differential-relay may be energized whenever the vertical or rotary side of the main calling line is grounded, aiter said line has been trunled to the connector, or may also become energized if both of said line-conductors are grounded at the same time. ln the latter case, the coils 335 and 336 reintorce or-auginent each other with their magnetic influences; but it the backbridge-relay 83st, after a line is called, should be energized while the main line-conductors of a calling line are connected through the repeater, as will be shown, or it they meet in any wan-y whatever, an electric current Will then pass from the side-switeh-wiper 303 through the ditlerential-winding 330 to the rotai'y side of the line and on to the vertical side, then through the winding 335 to the non-grounded terminal ot the battery, in which case the differential-relay is not energized. The windings 33T and 338 ot the back-bridge-relay are connected one with the vertical side of the main line and the other with the rotary side of the main line. The other end of the tir-st coil 337 is connected to the diferential-relay-spring Bill, which latter normally is found in electrical contact with the middle dierentiaLrelayspring 1:5 i0 that constitutes the non-grounded termina! of the battery. The other terminal of the winding 338 is permanently connected with the sicle-switcli-wiper 303, which latter, when in the third position, is connected with ground. Therefore, when the main lineconductors are connected through the called substation, a current will flow from the side-switch-wiper 303 through the winding 838 ot the baclr-bridge-relay to the rotary side of the main line, then to the vertical side and baclr through the second winding 337 to the non-grounded 'terminal of the battery. These windings, unlike the windings of the ditterential-relays, when the main lines are thus connected, reinforce or augment each other to energize the back-bridgerelay. The release of the tiret-selector, in a manner already clearly described, does not occur until the denergizing oi" the releasemagnet et the first-selector, but the release of the t nector, as plainly set forth, occurs iimnedisue'jif' upon the energizing ot its release-magnet. Should the connector-shaft be in a raised condition when the releasemagnet T365 is energized, the release-arma ture 2 0, as previously stated, then moves the double-flog 268 under' the release-lint: 269, which latter then catches the lug E374- and holds said double-dog out ot engagement with the shaft. Said shaft then being 'tree returns, tor the same reasons described in connection with the hrst-selector-shatt, to its normal or released condition. T he normalpostarin 259 of the connector has control of two springs 197 and 198 which are closed when the shaft is raised, and open when it is down.

ln Fig. Qrthe first-selector F2 that is associated with the called line is identical with the tiret-selector F1 of the calling line, and needs no explanation, since like parts are likewise represented. W hen reference is made to the parts oit said called tiret-selector it will be understood that their functions and constructions are the same as those already described for the first-selector F1. In the system under consideration, of course, it clear that there may be a multiplicity of sub-stations common to the central stations, each of which is connected with the central station by a line composed of two conductors, each of which lines has permanently allotted to it a first-selector. The firstselectors may be sub-divided into groups of one hundred, each with all corresponding line-banlcterminals ot a given group connected in multiple, and a similar arrange nient being followed in connection with the private-bank-terminals. For each level of lirst-selector-line-bank-terminals ten trunklines are provided which terminate in suitable switches arranged in groups. Therefore, `for each level to which a first-selectorshatt may be raised, the lineewipers are placed on a level with a diderent set of switches one of which may be selected ttor the purpose or reaching subscribers in diilerent numerical groups. Each iirst-selector is connected with a given set of bank-contactpoints in the banks of the connectors of the hundred to which said tiret-selector belongs, and when the first-selector comes into use a guarding potential is placed at the connector-private-banlr-contacts ot' the line of the calling lirs`=selector to prevent any calling` subscriber from calling-in on said line over the ,so-called normaltrunk-conductors that extend between the connector-banks and the first-selector.

To more fully understand the operations and circuits in connection with my invention, a description will now be given ot the apparatus and circuits brought into use in the system when one subscriber calls another subscriber, illustrated in Figs. l and 2. For example, when the subscriber at substation #7000 calls the subscriber at sub-station #2420, the subscriber at the calling sub-station 7#$7000 removes his receiver from the switch-hook 2 and causes the ground-springs 23 and Qfl to c me into contact and complete a circuit between the groundeterminal G3 and the conductors ll-00 and 01. Then the vertical-push-button 29 is pressed twice, and the rotary-button 30 once, again the first button 29 tour times, and the second button 30 once, then the button 29 twice, and the button 30 once, and for the last time the lirst button ten times,

llt)

and the last button once. When the spring 33 is forced onto the ground-post 22 twice in succession for the first time, the verticalline-conductor 402 is grounded twice, causing the vertical-line-relay 69 of the firstselector to become magnetized and attract its armature 71 twice. The energizing Current that passes through said vertical-linerelay at the time enters the line at the ground-terminal G3, then passes to the ground-post 22, and through the spring 33 to the vertical-line-conductor 402, thence through the vertical-side-switch-wiper 143, conductor 404, vertical-line-relay 69, conductor 405, bridge-cut-ofi're1ay-springs 79 and 80, conductors 406, 407 and 408 to the non-grounded terminal of battery B1 and to ground G1. As a result, the line-relayspring 73 is forced onto the ground-spring 75 twice, which operation closes a second energizing circuit through the vertical-magnet 85. The current in this second circuit enters the line at the ground-terminal G4 and then passes through the springs 75 and 73 to the conductor 409, and through the private-springs 127 and 126 and conductor 410 to the vertical-magnet 85, passing thence through the conductors 411, 412, 413 and 408 to the non-grounded terminal of battery B1 and to ground G1. The verticalmagnet 85 then attracts the vertical-armature 86 twice and raises the switch-shaft two steps. At the first step, of course, the release-link 95 is withdrawn from the double-dog 101, at which time the dog 103 engages with the circular teeth G0 and prevents the shaft from falling to its original position. So soon as the switch-shaft rises, the off-normal-spring 66 then closes with the grounded contact-point 68, at which instant and by which act the connector-private-bank-contacts that correspond to the line-conductors of the sub-station #7000 are connected with ground G5, which connection establishes a guarding potential for the line #7000, so that no subscriber may be able to connect with it after once the firstselector F1 of said line has been operated. After the Vertical-line-conductor is grounded twice the rotary-line-conductor 414 is grounded once through the spring 34. An electric current then flows through the rotary-line-relay for a moment, which magnetizes the said rotary-line-relay, causing the latter to attract its armature 72 once and force the spring 74 once against the ground-spring 75. The current then passes from G3 to the ground-post 22, thence through the spring 34 to the rotary-lineconductor 414, side-switch-wiper 144, contact-point 150, conductor 415, rotary-linerelay 70, conductor 416, springs 78. 79 and 80 to the non-grounded terminal of battery B1 and to ground G1. When the springs 74 and close together a second magnetizing circuit is completed through the privatemagnet The electric current in this case fiows from the grounded terminal G4 through the line-relay-springs 75 and 74, conductors 417 and 418 to the private-magnet 122, after passing through which it passes through the conductors 419, 413 and 408 to the non-grounded terminal of battery B1 and to ground G1. The privatearmature 121 being attracted once and restored immediately, the escapement-tooth 133 first clears the escapement-finger 138, which latter then falls against the second tooth 131, and when the armature returns to its normal position this latter tooth also disengages the said escapement-finger. At that instant, the side-switch is drawn into the second position by the retracting-spring 139, with the cam-lug 140 resting against the cam 56. It will be understood that the prongs of the bifurcated end of the link 160, that rest upon the T-shaped extremity of the double-dog releasing-arm 105, are of sufficient length to permit the said releasing-arm 105 to move from the position that it holds when the double-dog is held normally locked by the release-link 95, to the position it assumes when the said doubledog is released, without disengaging from said prongs. At the moment that the sideswitch passes from the first to second position a circuit is completed through the rotary-magnet 108 when the side switchwiper 141 closes with the contact-point 151. The current then Hows from the ground terminal G to the contact-point 151, through the side-switch-wiper 141 and conductor 420 to the rotary-magnet-coil 110. thence through the interrupter-springs 118 and 119 and through the second rotarymagnet-coil 109 to the conductors 412, 413 and 408 to the non-grounded terminal of battery B1 and to ground G1. The rotarymagnet 108 then attracts the rotary-armature 111 and forces the rotary-pawl 115 into engagement with one of the longitudinal teeth 59 causing the shaft to rotate one step. .lust at the time, or at the instant before the rotary-armature strikes the rotary-magnet pole-pieces, the rotary-dog 104 falls behind the first of the longitudinal teeth, in the manner already described, to prevent the shaft from returning to its normal position when the rotary-magnet becomes denergized at the instant that the interrupter-finger forces the interruptersprings apart and destroys the energizing circuit through the said magnet. This interruption occurs just at the time when the rotary-armature strikes the pole-pieces, or an instant later. When the rotary-pawl 115 advances to engage the longitudinal teeth, as described, the rotary-armaturefinger comes into Contact with the privatearmature 121, producing a depression of the latter at the same time that the rotary-paWl produces a rotation of the shaft. As the shaft begins to rotate, the cam 56 very soon passes out of reach of the cani-lug 140 and permits the escapement-finger 138 to fall against the tooth 134 before the rotary-arxnature-linger 129 has depressed the private-armature 121 too far. Very soon, however. the said tooth 134 is carried below the linger 138, which latter then falls against the upper tooth 132 just at about the time that the shaft-wipers are rotated onto the first contact of the second level of their respective banks. As soon as the energizing circuit through the rotary-mag net is interrupted, the rotary-armature then begins to return to its normal position, and the private-armature 121 as Well, following up the receding movement of the rotaryarmature-finger 120. Very soon the tooth 132 disengages the escapement-fnger 138 also, and the side-switch springs into third position with the escapement-finger 138 against the side-switch-stop 146. The shift ing of the sideswitch takes place just be fore the interrupter-nger permits the interruptor-springs 118 and 119 to rengage, so that by the time that they do rengage the energizing circuit that has been de scribed through the rotary-magnet has been destroyed between the side-sWitch-Wiper 141 and thtI contact-point 151. When the motion of the rotary-armature ceases permanently the operation of the first-selector comes to an end, the line-Wipers 53 and 54 having seized upon an idle trunk-line similar to the trunk-line the conductors 421 and 422 of which terminate at the tenth set of contacts of the second level of the same line-bank. The seized line is protected from further seizure by ,a guarding potential at the private-Wiper, and, therefore, at the first contact of the second level of the private-bank 51` and to all other private. contacts in multiple. Said guarding potential is established by reason of the connection between the ,grounded terminal of battery lill and said private-contacts, through the @round terminal GT, sidesrvitch-Wiper 142. conductor 423, back-release-relay 81,` conductor 424` and the private-wiper 55. Similarly, should any first-selector appropriate to its use the second trunk-line of the. same level a ,guarding potential will appear at the second private-contact of the second level of the privatebanl 51, as Well as at all other private-banks in multiple. And should a third first-selector seize the third trunk on the same level a guarding terminals of the second level of the privatebank. Therefore, if the first nine trunklinesl ofthe second level are busy a guarding potential is found each one of the first nine private-contacts of the second level of the private-bank 51. If this condition exists at the time that the calling subscriber grounds his rotarydineconductor by pressing button 30, the rotation of the shaft Will not terminate as soon as the Wipers have moved onto the first terminal of the level to which they have been raised. The first nine private-contacts being grounded, then when the calling; subscriber grounds the rotary side of the line the side-switch trips into second position in the manner described; but then the rotation of the shaft will begin, not to cease, until the Wipers have been carried beyond the last of the busy trunk-lines-in this case onto the tenth terminal of the second level of the banks in question. This operation talres place in the following Inanner: The energizing` circuit through the r0- tary-magnet being` closed, as Was pointed out, at the juncture when the side-switch- Wiper 141 engages with the contact-point 151, the rotary-armature is attracted by the i'otaryniagnet 108, and the shaft is rotated one step in the manner described, so that the line and private Wipers are rotated into engagement With the first terminal of the second level of their respective banks. At the same time the private-armature is depressed by the rotaryarmature-finger and the interrupter-springs 118 and 119, are, at the end of the stroke, separated by the interrupterfinger 117. There being;- a guarding potential at the first contact which the private-Wiper meets, a circuit is completed through the private-magnet 122, which entends from the grounded terminal of the battery B1 through the private-Wiper of Whatever first-selector is occupying` the first trunk of the second level in question, through the bank-multipling conductors to the contact-point with which the private-Wiper 55 has engaged, thence through said private-wiper 55, conductor 424, ivindinff, of the bacl. -release-re lay 81, conductor 423, side-svvitch-Wiper 142, contact-point 152, conductors 403 and 418 and private-magnet 122 to the non-grounded terminal of battery B1 and to ground G1. The private-armature is thereby retained in the depressed condition even after the energizing circuit is broken at the interruptersprings, and while the 1otary-arniati1re-fin ger 120 returns to its normal position in re sponse to the retracting tension of the rotary-armature retracting-spring 113, since the escapement-nger 138 is held by the upper foremost escapement-tooth 132. The side-sivitchwiper 141 being, therefore, retained in engagement with the grounded contact-point 151, as soon as the interruptersprings rengaae the energizing circuit through the rotary-magnet 108 is completed once more. As a result, the rotary-armature is attracted again, the shaft is rotated one more step, and the private-wiper 55 is moved onto the second terminal of the second level of the private-bank 51. Said second contact also being grounded, it follows that the energizing circuit through the private-magnet is still maintained, so that the side-switch is still not liberated when the rotary-armature again returns to its normal position. Clearly, then, the shaft will be rotated in a step-bystep manner as long as the private-wiper continues to meet with grounded privatecontacts. After having rotated onto the ninth contact, the private-wiper is rotated one more step into engagement with the tenth contact of the second level of the private-bank; but this last contact being devoid of guarding potential, as soon as the said wiper leaves the ninth contact, the magnetizing circuit that has, up to this time, maintained the private-magnet energized is broken. This occurs at just about the time when the rotary-armature is at the end of its attractive stroke; so that the private-.armature that has, up to this time,

eld the side-switch in its second position through the magnetizing force that has now disappeared from the private-Ina et, falls back upon the rotary-armaturenger and follows said finger as the rotary-armature returns to its normal position. Between the time that the private-armature is released by the private-magnet and the time that the rotary-armature fully regains its normal position, the escapement-fin er 138 which, during the rotation of the s aft, has been resting against the foremost tooth of the upper escapement-spring, disengages from said tooth and permits the side-switch to pass into the third position. It is then that the side-sWitch-wlper 141 leaves the contactpoint 151 and passes onto the contact-point 155. This disengagement occurs just before the interrupter-springs 118 and 119 ree'ngage, so that the circuit through the rotarymagnet is permanently broken in order that no further rotation of the shaft may take place during its use. The sideswitchwipers 143 and 144 having engaged with the ,contactints 157 and 158, the subscribers line-con uctors 402 and 414 are then extended through the respective Wipers and over the conductors 425 and 426 to the vertical and rotary line-wipers 53 and 54, respectively. Said wipers being at the time in engagement with the tenth contact of the second level of the line-bank the calling subscriber is thus placed in connection with the repeater R. It may be stated at this point that if, after the subscriber has begun to call. and before the rst-selector has trunked to the repeater, he should desire to discontinue his call he may interrupt the operation of the first-selector and sestore it by simply hanging up his receiver on the switch-hook 2. This may occur while the side-switch is either in the first or second position, it matters not. As a result of restoring the receiver, both sides of the main line w1ll be grounded simultaneously. The rotary and vertical line-relays and 69 will be magnetized at the same time, and as a result the release-magnet 98 of the firstselector will be energized and the firstselector will be restored. It has been described that in its action the release-camarm 3, as it passes down, when the receiver is restored, flexes the release-springs 25, 26 and 27 into contact for a moment. Of these springs the release-springs 25 and 26 are connected, respectively, with the vertical and rotary line-conductors, while the third release-spring 27 is connected to ground G3.

Therefore, as a natural result, the temporary engagement of these three springs sends a ground impulse over each side of the main line, with the effect upon the first-selectorline-relays already mentioned. The current through the vertical-line-relay, during the release. passes from ground G3 through the ground-springs 24 and 23, conductor 400, release-springs 27, 26 and 25, to the verticalline-conductor 402, and thence through said relay to the non-grounded terminal of battery B1 and toground G1. Through the rotary-line-relay 70 the current flows from the same ground Gr3 to the release-spring 27, thence through the release-spring 26 to the rotary-line-conductor 414, thence through the line-relay in question to the non-grounded terminal of battery B1 and to ground G1. Since the contact-points 149 and 153 associated with the vertical-side-switch-wiper 143 are connected together, and since the contact-points 150 and 154 of the rotarv-sideswitch-wiper 144 are connected together, it will be evident that it makes no difference for a release whether the side-switch is in first or second position, as the energizing circuits during the release, as pointed out in the conditions under consideration, will be the same. The fact is already familiar that when the rotary-line-relay is energized the private-magnet 122 is energized, as a result of which the latter` during its energization, maintains the private-springs 127 and 128 in contact. It is also familiar that when the vertical-line-relay is magnetized the private-spring 127 is connected with ground Gr4 at the line-relay-springs. It was shown that when said private-spring 127 was grounded. and while in contact with the spring 126. that the vertical-magnet was energized z but in this case. since said springs 127 and 126 are not in contact, but instead the springs 127 and 128 are in engagement, a different circuit is established that comprises the release-magnet 98. The energizing current in this circuit passes from the ground GfL to the private-springs 127 and 128, thence through the conductors 427 and 428 and the release-magnet 98, conductors 411, 412, 113 and 408 to the non-grounded terminal of battery B1 and to ground G1. Then the cam-arm 3 disengages the releasesprings, the line-relays 69 and 70 then become denergized, and as a result the release-magnet 98 becomes deenergized and the armature ot the latter, in regaining its normal position, restores the iirst-selectorswitch in a Well-known manner. 1t should be made clear that when the first-selectori shaft is rst operated, and when the oft-nornialspring 66 closes into electrical contact with the contact-point 68, a guarding potential is then established at the connectorpriVate-bank-contacts, through the so-called pri`fat e-normtl-conductor 129. The estarblishmont of this guarding potential is tor the purpose of preventing any other calling subscriber from attaining connection with the line #7000 over the normal-line-condnctors 430 and 1131 that terminate in the connector-banks, While the said line is malring the call. But when the shaft ialls to its normal position, when the switch is released, this guarding potential is destroyef'l at the instant that the normalpost-arm. 63 forces apart the springs 68 and 00. However, since the subscriber continues his call instead oit' releasing he then, zitter pressing the pnslrbutton 29 twice and the push-button 30 once, continues by pressing the push-button 29 again tour times. V.1g ,'ain the verticaldiire-conductor L102 is grounded tour times momentarily. The first-selector-line-relays and having been out ofi' ot' the liricv at the instant that its side-switch passes into third position, and the line being connected then With the repeater il, the grounding ot the Vertical-linecondnctor energizes the line-relay 200 and the ditlerontialwrelay 209 of the repeater R. The cmfrent in this case, after reaching the `verticalline-conductor and the vertical-sit eswitchiP-#iper 11i-,l o1' the first-selector, passes thence through the contact-point 157, conductor 125, the yerticaldine-Wiper 53, trnnlrcondncor 421, conductor 1132, linerelfy 200, (fondu. :or Winding 210 ot the d.,` ,rential relay 23'9, conductors 13e/t, and 430 to the non-grounded terminal of battery B1 and to ground (Vfl-1. The energization ot the line-relay 200 causes the spring 2044 to be pressed onto the spring 205, While the energization of the diiierential-relay vforces the springs 218 and 219 apart and closes the springs .21 and The line-rclay-spring 20st, boing connected directly with the inten echange trrnik-condnctor 337, through the conductor 1138, and the spring 205 being connected to ground G8, the engagement of the springs 2041 and 205 therefore connects the said trunk-conductor 437 with ground, Since the said relay 200 is energized four times, the said trunk-conductor becomes grounded four times. The object in separating the springs 218 and 219 at the saine time that the trunk-conductor 437 is grounded is to prevent the ground impulses to said trunk-conductor from being' conducted to the rotary-trunk-conductor L139. rlhe circuit hrough which the Vertical-trunir-conductor 37 reaches the ground 'terminal G8 extends from said trunk-conductor through the conn ductor 438, springs 2041 and 205, conductor '1140, springs 224i and 220, to the ground terminal GS. rI'his ground connection would reach the rotary trunk s conductor 439 throng-h the pole-changing-relay 213, conductors 4111 and 1412, springs 218 and 219, conductor 1l-,8 to the rotary-trunlcconductor 139, were it not that the springs 218 and 219 are kept apart` The results produced by grounding the verticaltrunk-conductor 137 will be desc 1ibed herein. After the `verticalbutton 29 has been operated as described, the rotarysbntton 80 is operated once. The latter, as a result, connects the rotary-lineconductor 114; to ground for a moment. In this case, the rotary-line-relay 201 and the dillercntial-relay 209 oit the repeater R are energized simultaneously by a current tloW- ing from the ground G3 to the rotary-linecondnctor 411i, and to the side-switch-Wiper 144s, thence to the contact-point 158, conductor 4126, rotary-line-Wiper 54, trunk-conductor 4122, conductor 11414, rotary-line-relay 201, conductor 445, Winding 211 of the differential-relay 209, conductors 446 and 447, springs 212 and 2111-, conductor 148 to the non-grounded terminal of battery Bl and to ground G1. rlihe energizing ot the differential-relaiY .'ictnates the springs under its control as before, while at the saine time the rotary-line-relay .201 forces the springs 205 and 20G into Contact, rnd thereby grounds the rotarytrunk-conductor 189. The connection between ground and said `trnnl-conductor 4,89 is made from the ground-termi nel GS through the springs 226V and 224, conductor 440, springs 205 and 206, conductor 449, springs and and conductor 450 to the said trnnlnconductor fri-39. The separation of the said springs 218 and 219 by the differential-relay 209 prevents the vertical-trnnlr-conductor 1137 'from being grounded,r together with the rotarytrunk-conductor 439, at this time. The engagement of the springs and 220, each time that the dit- :terential-relay 209 has been energized licretofore, plays no part, and is oi= no significance, save during' a release which Will be described. After the first-selector F1 has trunked to the repeater R, the switches may be released again at this point of the calling operation by restoring the receiver to the switch-hook. The simultaneous grounding of the vertical and rotary line-conductors will produce a simultaneous energization of the vertical and rotary line-relays 200 and 201 over circuits that need not be further described. The windings of the differential-relay 209 are so arranged that when the line-conductors are grounded current passes through them in such a direction that the said windings reinforce or augment each other magnetically, and, therefore, the said differential-rela57 becomes energized at the same time that the line-relays 200 and 201 become energized. This being the case, the differential-relay-springs 221 and 220 are brought into contact at the same time that the repeater trunk-release-springs 207 and 208 are forced together by the simultaneous energization of the said relays. The simultaneous engagement of said two sets of springs establishes an energizing circuit that includes the first-selector-back-release-relay 81. The current in this circuit flows from the ground terminal G7 of the first-selectorside-switch, thence to the contact-point 156 and through the side-switch-wiper 142, conductor 423, through the back-release-relay 81, conductor 424, private-wiper 55, releasetrunk-conductor 451, trimk-release-springs 207 and 208 of the repeater R, conductor 452, resistance-coil 235, springs 221 and 220, conductors 435 and 436 to the non-grounded terminal of battery B1 and to ground G1. The back-release-relay 81, upon being energized, forces the springs 83 and 84 into elecr trical contact, and thus in turn a second circuit including the release-magnet 98 of the first-selector is completed. This circuit extends from the ground terminal G9 through the springs 83 and 84, conductors 453 and 428, release-magnet 98 to the non-grounded terminal of battery B1 and to ground G1. As soon as the release-springs at the substation #7000 disengage, the current through the repeater-line-relays 200 and 201 and the differential-relay 209 is interrupted,

and the energizing circuit through the backrelease-relay 81 is opened at the differentialrelay-springs 221 and 220, and at the release-springs 207 and 208. The back-release-relay 81, on becoming denergized, destroys the energizing circuit through the release-magnet 98 which at once permits its armature 97 to return to normal position and produce the release of the first-selector. It should be noted that when the line-relays 200 and 201 are energized during the release, under these conditions, the vertical and rotary trunk-conductors 437 and 439 are simultaneously grounded when the springs 204 and 206 are forced onto the spring 205. The subscriber not Wishing to release, however, continues his call; but before proceeding, the effect of grounding the trunk-conductors 437 and 439 will be considered. Since the said trunk-conductors are directly connected with the second-selector S in the same manner that the line-conductors 402 and 414 of the sub-station #7000 are connected with the first-selector F1, the' grounding of said trunk-conductors, as described, results in the operation of the second-selector in the identical manner in which the firstselector F1 is operated when the buttons 29 and 30 are pressed. The groundin of the vertical-trunk-conductor 437 .energizes the Vertical-line-relay 164, and the current iows from the ground terminal G8 to the verticaltrunk-conductor 437, as stated, over which it flows to the side-switch-wiper 165, contact 166, and through the conductor 454, vertical-line-relay 164, conductors 455, 456 and 457, to the non-grounded terminal of battery B2 and to ground G2. The line-relaysprings 167 and 168 are forced together in the usual manner, and a circuit through the vertical-magnet 169 is established that permits a flow of current from the ground terminal G10 through the springs 168 and 167, conductor 458, private-springs 170 and 171, vertical-magnet 169 to the non-grounded terminal of battery B2 and to ground G2. The resulting energization of the Verticalline-relay four times causes the verticalmagnet 169 to become energized four times, and as a result the switch-shaft is raised four steps in a manner that needs no eX- planation. At the end of this operation, of course, the switch-wipers 173, 174 and 175 will be found opposite the lirst contact of the fourth level of their respective banks. The grounding of the rotary-trunk-conductor 439, following the grounding of the vertical-trunk-conductor 437, produces an operation of the rotary-line-relay 178. The current in this case, after reaching the rotary-trunk-conductor 439 from the ground terminal G1, as described, passes on to the side-switch-wiper 179, contact-point 180, conductor 459, rotary-line-relay 178 to the non-grounded terminal of battery B2 and to ground G1. This relay, being energized momentarily, energizes as a result the privatemagnet 181 once at the instant that the springs 182 and 168 are forced into contact. The current here flows from ground G10 through the springs 168 and 182, conductors 460 and 461, private-magnet 181 to the nongrounded terminal of battery B2 to ground ,12. The private-magnet, by actuating its private-armature once, permits the sideswitch to pass into second position, at which time the side-switch-wiper 183 passes from engagement with the contact-point 184 onto the grounded contact-point 185. The union of said side-switch-Wiper with the said grounded contact-point produces an actuation of the rotary-magnet 186 by means of the current that flows from the ground terminal G11 to the contact-point 185, thence through side switchwiper 183,

conductor 462, rotary -inagnet 186 to the non-grounded terminal of battery B2 and to `ground G2. Assuming that the first nine tru nits of the fourth level 01"' the secondselector are busy, the rotation of the shaft, in a manner clearly described in connection with the Vfirst-selector F1, continues until the shaft has been rotated ten steps, placing the switch-wipers in connection with the tenth terminalv ot the fourth level of the banks. Of course, the 1 nivate-magnet during the rotation of the private-Wiper over the busy contacts is maintained energized, as was described in connection with the first-selector. The current here passes naturally from the busy contacts to the private-wiper 175, through the baclr-release-relay 187 to the side-switch-wiper 188, which latter, being in second position, extends the circuit through the contact-point 189 and through the private-magnet 181 to the non-grounded terminal or battery B2 and to ground G2. The` line-wipers 173 and 174 are then, of course, in electrical connection with the trunk-conductors 463 and 464, and the private-wiper 17 in engagement with the release-trunkconductor 465. The side-switch-wiper 188, while in third position, being connected to ground G12 through the contact-point 100, the usual guarding potential .is supplied to the private-wiper 175, and as a result to the private-contact with which it is connected, in order that no other trunk-seeking second-selector may be able to seize upon the truninline-conductors 463 and 464. The second-selector S, of course, may be released it the trunk-conductors 437 and 439v are grounded simultaneously while the sideswitch is in the first or second position, in the saine manner that the first-selector is released. when both sides of the main line are grounded. This will occur, as has been pointed out, if the calling` subscriber hangs up his receiver at that stage of the call when the said second-selector-side-switch is in first or second position. It will be clear that if the vertical and rotary line-conductors 402 and 414 are grounded simultaneously 4while the first-selector, repeater and second-Frlector are connected, and while the second-selector-side-switch is either in first or second position, the {inst-selector will be released as described, during which release the trunk-conductors 437 and 439 will be grounded simultaneously, producing at the same time a release of the second-selector. The switching of the second-selector onto the trunlr-conductors named places the substation #7000 in direct communication with the connector C, which latter will in turn be operated when the calling subscriber next Dresses his button 29 twice. The around-- ing of the vertical-line-conductor will cause the verticaldine-relay 200 and the differential-relay' 209 of the repeater R to be ener- Igized twice. As a result, the vertical-trunkeonductor 437 becomes grounded twice; and said trunk-conductor having been connected through to the connector C, it is evident that the vertical-linc-relay 318 and the diti'erential-relay 333 of the latter will be energized twice by a current flowing from the ground terminal G8 at the repeater to the vcrtical-trunlr-conductor 437, thence through the side-switch-wiper 165 of the second-selector to the contact-point 191, thence through the conductor 466, vertical-line-Wiper 173, vertical-trunlr-conductor 463, Vertical-linerelay 318 of the connector C, conductor 467, winding-.335 of the dierential-relay 333, conductors 468, 469, 470 and 471 to the non-grounded terminal of battery B2 and to ground G2. The Vertical-line-relay, after attracting its armature 319, closes the springs 320 and 321 into electric contact and establishes an energizing circuit through the Vertical-magnet 261 o1E the connector. The energizing circuit passes from ground G1d through the springs and 320, conductor 472, private-springs 291 and 290, conductor 473, side-switch-Wiper 302, contactpoint 306, conductor 474, Vertical-magnet 261, conductors 470 and 471 to the nongrounded terminal of battery B2 and to ground G2. The vertical-magnet, on attracting its armature twice in the same man, ner that the previous selectors have operated their shafts, raises the shaft 252 two steps, and 'places the connector-wipers 253, 254 and 255 opposite the first contact of the second level of their corresponding banks. The calling subscriber then presses the rotarybutton 30 once, grounds the rotary-line-conductor 414 once, energizes the rotary-linerelay 201 and dilierential-relay 209 of the repeater R once, which former in turn grounds the rotary-trunlr-conductor 43S)I once. -Said conductor extending to the connector' causes the magnetizing of the rotaryline-relay 324. The current in this last circuit fiows from ground G8 to the rotarytrunk-conductor 439, through the secondselcoter-sideswitch-wiper 17 9, contact-point 192, conductor 475, rotary-line-wiper 174. trunk-conductor 464, rotary-line-relav 324, conductor 476, winding 336 ot' the difierential-relay 333, conductor 477, back-bridgerelay-sprinss 343 and 344, conductors 469, 470 and 471 to the non-grounded terminal of battery B2 and to ground G2. The. connector-line-relay-sprinxrs 326 and 321 being therebt7 connected together the private-magnet 281 is energized bv a current Rowing from the .around G13 through said snrinqs and 326, conductor 478. private-magnet 281., conductors 479 and 477` back-bridgerelay-snrings 343 and 344 to the nongrounded terminal of batterv B2 and to l,Q1-mund G2. The connector-private-magnet being energized once attracts its armature once, which latter permits the connectorside-switch to pass to second position, the side-switch-wiper 302 passing from the oontact-point 306 onto the contact-point 307, and the side-switch-wiper 303 from the contact-point 309 onto the contact-point 310. The shiftin of the side-switch-Wiper 302, as stated, pro uces a change in circuits in the connector, then when the vertical-button 29 is pressed ten times for the last digit, and the energization of the vertical-line-relay 318 results ten times, over a circuit already pointed out, the rotary-magnet 277, instead of the vertical-magnet 261, is operated when the springs 320 and 321 are brought into contact. Each time that the springs 320 and 321 close, a current passes from the ground terminal G13 through the springs 321 and 320, through the rivate-springs 291 and 290 to the side-switch-wiper 302, passing through which it then extends through the contact-point 307 to the conductor 480, thence through the rotary-magnet 277 to the non-grounded terminal of battery B2 to ground G2. At each pulsation, the rotary-magnet attracts its armature 278,

`rotating the shaft 252 one step at a time,

sliding the wipers 253 and 254 along the second level of the bank with which they engage. At the end of the tenth pulsation, the wipers are landed onto the tenth contact-terminals of the second level. For the last time the rotary-push-button 30 is pressed once, the rotary-conductor 414 is grounded once, the rotary-line-relay 201 and differential-relay 209 of the repeater are energized, and as a result the rotary-trunkconductor 439 is grounded once. Again the rotary-line-relay 324 of the connector is energized once, the said relay in turn producing the operation of the private-magnet 281 that permits the side-switch to pass* into third position with the side-switch-wipers 302, 303, 304 and 305 in contact with the contact-points 308, 311, 314 and 317, respectively. The engagement of the sideswitch-wiper 303 with the contact-point 311 places a guarding potential at the private-wiper 255, and at the tenth private-contact of the second level of the private-bank 251, to preclude any other connector from entering into connection with the called line #2420. It will be understood, of course, that the same guarding potential exists at all other private-bankcontacts in multiple with the private-bankcontact mentioned. The closure of contact between the side-switch-wipers 304 and 305 and contact-points 314 and 317 respectively, connects the extended subscribers line-oonductors 463 and 464 through the condensers 345 and 346 with the vertical and rotary line-wipers 253 and 254. and, therefore, with the normal-conductors 481 and 482 that constitute the terminals of the called sub-station #2420. rlhe calling first-selector, it will be remembered, places a guarding potential over its own line at the connectorprivate-bank-contacts that correspond to the substation #7000, at the instant that the off-normal-spring 66 comes into contact with the grounded spring 68. Later, and at the instant that the connector seizes on the called subscribers normal-conductors 481 and 482, the calling connector places a guarding potential over the called line at the instant that the side-switch-wiper 303 engages with the contact-point 311. Evidently, then, a line is protected by a guarding potential, either when calling or when called, in the former case by operations in the first-selector, and in the latter case by the connector. The establishment of a guarding potential for the called line #2420 not only protects it from further seizure, but also forces a current through the bridgecutoff-relay 350 of the called first-selector F2, in order that the latter, by its armature, may separate the bridge cut ofl:` relay springs 351, 352 and 353. The separation of the said springs from each other destroys a bridged circuit through the vertical and rotary line-relays 354 and 355, and that normally extends across the line-conductors 483 and 484, and at the same time interrupts a connection between said relays 354 and 355 and the non-grounded terminal of the battery B2, which terminal is directly connected with the spring 353. Since the conductors 483 and 484 are included, one on each side of the main talking circuit. as will hereinafter be disclosed. it is desirable to remove all unnecessary bridges from across said conductors, for obvious and other reasons to be described, and at the same time to remove all possibility of the vertical and rotary line-relays being energized when a rmging current is projected to the called sub-station, so that no undesirable interruptions may take place thereby. The energizing circuit through the bridge-cut-oif-relay 350 extends from ground G to the connector side switch contact point 311, side-switch-wiper 303, conductor 485, private-wiper 255. private-normal-conductor 486, spring 356. contact-point 357, conductor 487, and bridge-cut-of-relay 350 to the non-grounded terminal of battery Bz and to ground G2. In each preceding case where the rotary and vertical line-relays 318 and 324 have been energized, the differential-relay 333 has been energized also. but it has had no part in the useful operations of the switch as yet. The connection between the calling and called line having been established. the calling` party is in a position to signal the called line by means of his signaling button 12. But before going any further it will be explained that if for any reason the called line is busy at the time that the calling subscriber grounds the rotary-liric-conductor ell-Gl for the last time, to trani-lier the connector-side-switch from second to third position, the connector necessarily is released. For instance, it the line E20 has been called by another con-- nector, there Will be a guarding potential at the tenth private-contact ot the second lci'el oil the private-bank 251, corresponding to the line oit thV sub-station ll-2420. Or, on the other hand, if the first-selector F2 of the called line is being used, and the shalt or' said tiret-selector olli-normal a result, the same private-bank-contact Will be connected to ground from the instant that the normal-post-arm 358 permits the oli'- normal-spring 356 to engage with the grounded contact-point 359. @aid guarding potential will reach the prive-te-banl 0ll the connectzu' by Way of the private-normalconduct r LLSG. it any rate, it the privatewiper so linde a guarding potential at the tenth contact olf the second level ot the private-br ult 251, at the instant that the calling subscriber grounds his rotary-line-conductor 111/ Altor the last time, it follows that instead the side-s uitch being tripped to Y.tion the connector will be released because the energization of the private magnet T281 as a final result ot grounding the rotarydine-conductor 1111i sets up an energizing circuit through the release-magnet oii'the connector when the arg-mature o'l the said private-magnet forces the springs 202 and 200 into contact, The energizing circuit through the release-magnet allows the current to flow from the grounded 'terminal of the battery to the tenth contact oit' the second level oit the connector-private-bank through the private-Wiper Q55, conductor 485, side-snitch-Wiper 303, contact-point 310, conductor ii- 88, primte-springs 292 and i293, conductors 89 and i90, release-magnet Q05, conductor 191, springs l-l and 34,0, to the non-grounded terminal battery and to ground G2. lt Will be noticed that i -cireuit passes through the springs 310 ot the dilerential-relay 333, Whicn springs are normally apart. But it will be remembered that the said differential-rela)v becomes energized Wnen the calling subscriber :#:7000 grounds the rotaryline-coinluctor Dit Therefore, at the same time that the prieate-magnet close hc private-springs and 2,3, the ditlierentialrelay closes the said springs fB-lO and 311-2. The cf@hector-release ui Duet being energized, the release-erinture 206 inoyes the double-dog 268 so that the lug E27-'l is caught and held in the aperture Q76 on the end of the reirme-link. Ot course, when the dou- Q57. rllfen the shaitt is ilree to be rotated back to its normal rotary position, by the tension of the coiled spring 260, until the normal-post-arm 259 strikes the normalpost 3-17 llt that instant the shaft-support 84S enters the slot or groove 349, and the shaft ot necessity then falls to its normal position. rEhe release-armature, When it rotates the double-dog 208, at the same time driyes the side-switch to its about the pivots of the latter, by means of the side-sWitch-link 301 and the releasearm 273. rl`his latter, by pressing the toriner bach, forces the escapement-linger 295 baclr between the escapeinent-springs 283 and 28st, which latter is then caught behind the rearmost lower tooth 287 Where it remains until the connector comes into use again. The restoration of the connector-shaft takes place While the release-mag'- net 265 is in an energized state; but, since the energizing circuit through said magnet comprises the private-Wiper 255 and the side-switch-iyiper 303, it will be evident that as soon as the shaft begins to rotate to its normal position the energizing circuit through the release-magnet 265 will be broken as soon as the said private-Wiper 255 leaves the priiate-contact-point with which it has been engaged. The energizing circuit is also interrupted at the sideswitch-Wiper 303 When the latter is forced into its first position. The subscriber then, thinking he has established connection, presses the signaling button 12 at his substation, with the result that the spring 11 is separay ed. from the contact-point 10 and closed in connection with the grounded contact-point The said. spring 11 being in direct electrical communication with the vertical-hne-conductor 402, through the primary springs 13 and 14, and through the contact-point 31 and spring 33, it follows that the pressing of the button 12 grounds the vertical side of the line. The groundinO` ot the ver ical-line causes the energizing o; the connector-yertical-line-relay 318 in the usual manner; and since the connector-sideswitch is in first position, the connector-yertical-magnet 201 is energized, when the linerelay-springs 320 and 321 are pressed into contact through a circuit that is already familiar. As a result, and for reasons viously described, the shaft of the connector is raised and the springs 198 and 19'? *which it controls are brought into contact. The engagement of these two parts completes a busy circuit through which the busy signaling current is transmitted to the calling sub-station, which current may originate in any suitable apparatus, such as thaJ represented at F, Fig. 2, which comprises a coil 362 in which latter the said busy current isinduced. The. subscriber, having een instructed, will understand that the line he desires is busy. This busy current passes from the coil 362 to the conductor 1952, through lirst position, A 

